Heat release zones in turbulent, moderately dense spray flames of ethanol and biodiesel

Abstract

This paper extends the application of laser-induced fluorescence imaging of OH & CH2O (LIF-OH-CH2O) to provide a measure of heat release zones in turbulent, moderately dense spray flames of ethanol and biodiesel fuels. A custom filter is used to remove interference from stimulated Raman scattering arising from the liquid fragments. Mie scattering is measured jointly on a separate camera to co-locate the fluid fragments with respect to the reaction zones. It is found that while the overall spray flame structure is similar to that of a turbulent gaseous diffusion flame, additional complexities arise due to the continuous release of fresh fuel vapor from the evaporating fragments. Structures referred to as burning rings of different sizes are observed, and these are ignited by interfacing with a hot edge before they grow, propagate, and burnout. Statistics on the occurrence of these rings, with and without clouds of liquid fragments within them, are presented. These findings are common to both ethanol and biodiesel, although measurements in the latter were affected by strong fluorescence interference from the excited components in the biodiesel blend.